Slow relaxation of the magnetization observed in an antiferromagnetically ordered phase for SCM-based two-dimensional layered compounds.

Two-dimensional layered compounds with different counteranions, [{Mn(salen)}4 C6](BF4 )2 ·2(CH3 OH) (1) and [{Mn(salen)}4 C6](PF6 )2 ·2(CH3 OH) (2) (salen2- = N,N'-bis(salicylideneiminato), C62- = C6 H12 (COO)2 2- ), were synthesized by assembling [Mn(salen)(H2 O)]X (X- = BF4 - and PF6 - ) and C6 H12 (CO2 - )2 (C62- ) in a methanol/2-propanol medium. The compounds have similar structures, which are composed of Mn(salen) out-of-plane dimers bridged by μ4 -type C62- ions, forming a brick-wall-type network of [-{Mn2 }-OCO-] chains alternately connected via C6 H12 linkers of C62- moieties. The counteranions for 1 and 2, i.e., BF4 - and PF6 - , respectively, are located between layers. Since the size of BF4 - is smaller than that of PF6 - , intra-layer inter-chain and inter-plane nearest-neighbor MnMn distances are shorter in 1 than in 2. The zigzag chain moiety of [-{Mn2 }-OCO-] leads to a canted S = 2 spin arrangement with ferromagnetic coupling in the MnIII out-of-plane dimer moiety and antiferromagnetic coupling through -OCO- bridges. Due to strong uniaxial anisotropy of the MnIII ion, the [-{Mn2 }-OCO-] chains could behave as a single-chain magnet (SCM), which exhibits slow relaxation of magnetization at low temperatures. Nevertheless, these compounds fall into an antiferromagnetic ground state at higher temperatures of TN = 4.6 and 3.8 K for 1 and 2, respectively, than active temperatures for SCM behavior. The spin flip field at 1.8 K is 2.7 and 1.8 kOe for 1 and 2, respectively, which is attributed to the inter-chain interactions tuned by the size of the counteranions. The relaxation times of magnetization become longer at the boundary between the antiferromagnetic phase and the paramagnetic phase.